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Re: Big differences in plans between 8.0 and 8.1

From: "Chris Hoover" <revoohc(at)gmail(dot)com>
To: "Gabriele Turchi" <gabriele(dot)turchi(at)l39a(dot)com>
Cc: "Joe Conway" <mail(at)joeconway(dot)com>, "Michael Fuhr" <mike(at)fuhr(dot)org>, pgsql-performance(at)postgresql(dot)org, "Marco Colombo" <marco(at)esiway(dot)net>
Subject: Re: Big differences in plans between 8.0 and 8.1
Date: 2006-07-17 20:19:14
Message-ID: 1d219a6f0607171319k731ae186wc85cdca45851a51@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
Just turn on autovacuuming on your 8.1 database.  You can tune the vacuum
and autovacuum parameters to minimize the impact to  your system.  This is
the optimal route to take since PG will maintain the tables for you as
needed.

HTH,

Chris

On 7/15/06, Gabriele Turchi <gabriele(dot)turchi(at)l39a(dot)com> wrote:
>
> Il giorno sab, 15/07/2006 alle 13.04 -0700, Joe Conway ha scritto:
> > Gabriele Turchi wrote:
> > > Running an ANALYZE really change the plan, now it is fast as before
> > > (8.0).
> > >
> > > On the production system a VACUUM FULL ANALYZE is run every morning
> > > after a clean-up, when the "registrazioni" table is empty. During the
> > > day this table fills up (about 500 record any day), and apparently the
> > > performances are free-falling very quickly. This behaviour has not
> > > changed between the old and the new installation.
> > >
> > > Can you suggest an easy way to collect and keep up-to-date these
> > > statistics in a very low-impact way?
> > >
> >
> > Why not just periodically (once an hour?) run "ANALYZE registrazioni;"
> > during the day. This will only update the statistics, and should be very
> > low impact.
> >
>
> This is my "solution" too... but: is enough? Or else: there is a better
> way to do this? If the performance in the better case is 50 times faster
> than the worse case, during an hour (50/100 record inserted in
> "registrazioni") how much the performance can fall before the new
> "ANALYZE" is run? Otherwise, running ANALYZE more frequently can badly
> affect the overall performance?
>
> A so big difference in postgres performance, can be considered a bug or
> a over-optimization in the plan making? Why (at least apparently) the
> 8.0 version is not affected?
>
> > HTH,
> >
> > Joe
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 6: explain analyze is your friend
>
> Thank you all very much,
> Gabriele
>
>
>
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